Trump's statements in Helsinki were "very much counter to the plan," The Washington Post reported on Monday, citing a source from the administration.
According to the newspaper, aides gave Trump about 100 pages of briefing materials urging him to assume a tough stance toward Putin, but the president ended up ignoring most of the notes.
The US president was reportedly unhappy with the indictment of 12 Russians over alleged election interference, announced by the US Justice Department on Friday.
Trump met Putin in Helsinki on Monday for a one-on-one discussion that lasted over two hours. This was followed by a dinner with each others' advisers and a joint press conference.
At a joint press conference on Monday, Putin said that Russia might allow US officials to be present at questionings of Russian nationals suspected by the US authorities of illegal activities. Special Counsel Robert Mueller's probe into alleged Russian meddling could send a relevant request to Russia, Putin said.
However, Trump told Fox News that Mueller was unlikely to take the Russian authorities up on the offer.